1. Field of the Invention
This invention relates to aircraft control systems and, more particularly, to systems for limiting the maximum amount of reverse thrust which may be made available in accordance with different operating conditions of the aircraft.
2. Description of the Prior Art
Thrust reversing systems are commonly used on passenger and the larger cargo carrying jet aircraft. These thrust reversing systems are provided in order to permit the aircraft to decelerate more rapidly without such heavy dependence upon the wheel braking systems, once the aircraft are on the ground. One such system which is in common use has a plurality of deflector buckets that are moved into position in the jet exhaust when operation in the thrust reversing mode is desired. Once the thrust reversing system is in the activated position, the engine power control levers are moved to an advanced power setting and the engines wind up accordingly with the thrust now being deflected forward by the deflector buckets so that the desired reverse thrust is developed.
Special aircraft are now being developed for transporting cargo and/or passengers into landing fields shorter in length than those used by conventional aircraft. Known as STOL (Short TakeOff and Landing) aircraft, these planes need to be able to reduce their speed in the air with greater deceleration than is possible with available flap braking systems. Thrust reversing from the engines is available, as it is for deceleration once the aircraft has landed, but it is necessary to limit such thrust reversal to a greater degree than is required or even desired for thrust reversing after landing. If thrust reversal is to be employed during the landing approach or at any other time when the aircraft is airborne, it is important that the pilot be able to set the engine power control levels in the maximum thrust reversal position without having to look to determine the proper maximum power setting in the thrust reversal position. This calls for some kind of a lever stop mechansim in the power control system. However, a higher power setting is called for in use of the thrust reversal system after landing, which means that a different stop position is needed for thrust reversal after the aircraft has landed.
In-flight thrust reversal requires a reliable means of limiting the engine power control setting to prevent excessive reverse thrust power with possible damage to the structure and reduced operational reliability. The reverse thrust limiter must be capable of engaging or disengaging the engine power control system in a manner which precludes jamming or unsafe operation at any position of the throttle. Variation of the reverse thrust limiter position with temperature or power control system friction should be minimized in order to insure sufficient, but not excessive, power in in-flight thrust reversal operation.